CNIDARIA AS THE ONLY COELENTERATA 21 



origin of Ctenophora which has now been accepted by- 

 numerous zoologists, e.g. Sir Gavin de Beer (1954 a), it has 

 now become completely clear that Ctenophora cannot be 

 simply considered as Coelenterata that have no cnidae (Acni- 

 daria). Nevertheless, such an interpretation can be frequently 

 encountered. The Ctenophora are not Coelenterata and they 

 are not directly related to Cnidaria even if there is some relation- 

 ship between the two. Later we shall try to show in more 

 detail that the Turbellaria, the original form out of which 

 all Eumetazoa have developed, are also the starting point of 

 many other Am.eria (lower invertebrates), even of molluscs. 

 All these groups represent independent units as is true also 

 for Cnidaria and Ctenophora. Yet it will not do to establish 

 special phyla for these groups ; the highest systematic category 

 (taxon) must be reserved for large groups that are basically 

 different from each other. I will return to the discussion of 

 this problem later in the present study. 



It should be remarked in passing that unknown to me, 

 I was not the only person who tried to derive Ctenophora by 

 way of neoteny from the planktonic polyclad larvae. A similar 

 interpretation of the origin of Ctenophora has been proposed 

 by W. Garstang (cf. J. I. Brooks, 1954) at approximately the 

 same time that my thesis was published. Yet the form in which 

 that interpretation appeared is somewhat unusual for a scien- 

 tist: it was in a poem (Comic Verses) which was first pub- 

 lished in 1951 by A. C. Hardy (1954). Nevertheless, this does 

 not change the fact that an idea has been conceived according 

 to which the origin of Ctenophora must be sought in Miiller's 

 larvae that remain in the plankton and whose evolution is 

 influenced by neoteny. 



It has been now generally accepted by all zoologists that the 

 Spongiae represent a blind side branch of the animal kingdom, 

 which means that no other higher type of animal has been 

 developed from them. We have, therefore, no further interest 

 in the Spongiae. We shall return to discuss them only when we 

 deal with the problem of the origin of Metazoa. On the other 

 3 



